Field of the Invention
The present disclosure relates generally to ceramic materials, catalysts and methods for using them, such as methods for converting sugars, sugar alcohols, and glycerol to commercially-valuable chemicals and intermediates.
Technical Background
Zirconium oxide has been used as a support material in the field of chemical catalysis because of its high physical and chemical stability and moderately acidic surface properties. Nonetheless, the use of zirconium oxide as a supporting material for heterogeneous catalysts has limited application due to its relatively high cost and difficulties in forming certain shapes from. Furthermore, the zirconium oxide is especially susceptible to undergoing a phase transition that results in loss of surface area and pore volume. This reduces the strength and durability of the zirconium oxide. To counteract these phase transformation effects, stabilizing agents are used to inhibit phase transformation from the preferable tetragonal phase to the less desirable monoclinic phase. Previously used stabilizing agents include, for example, silicon oxide, yttrium oxide, lanthanum oxide, tungsten oxide, magnesium oxide, calcium oxide, cerium oxide, chromium oxide and manganese oxide.
Physical and chemical stability is a major concern in the application of heterogeneous catalysts in aqueous phase reactions. Traditional SiO2 or Al2O3 based catalyst supports are prone to disintegration or attack when used in an aqueous solution, which usually results in loss of mechanical strength of the catalyst body that is targeted for a long-term industrial application. In laboratory and industrial applications, the mechanical strength of heterogeneous catalysts is generally evaluated by crush strength, wherein increasing crush strength values are generally indicative of improved mechanical strength of the support or carrier. Use of zirconium oxide promoted with chromium oxide promoter materials yields a zirconium oxide-based support or catalyst with improved physical properties for extrusion and/or use as a carrier or support for a catalyst in industrial applications performed in an aqueous environment. Chromium oxide-promoted zirconium oxide support or catalyst materials typically demonstrate no leaching into an aqueous solution, improving the mechanical strength and stability of the support/carrier or catalyst in various aqueous phase applications.
However, use of chromium-containing materials, especially chromium(VI) containing materials, is less desirable because of their toxic, corrosive, and carcinogenic properties. Manganese-containing materials are a viable alternative to chromium-containing materials, but their use as catalyst materials can often be limited to aqueous phase reactions with a product pH above 6. There remains a need environmentally nonhazardous materials that are also stable for aqueous phase applications at a wide range of pH values.